The present invention relates to an application of low-temperature poly-silicon thin film transistors (TFTs) and, more particularly, to a field emitting display (FED) uniting TFTs and carbon nanotubes.
The maturity of semiconductor technology leads to the progress and development of the realm of vacuum microelectronics, wherein the vacuum microelectronic devices made of silicon are most valued. Various kinds of field emitting arrays have been widely studied. In order to let field emitting arrays be of practical use, the development of field emitting cathodes must tend to low operational voltage and high efficiency. Therefore, the surface work function or the geometrical structure of the field emitting cathode must be as small as possible.
FIG. 1 shows a prior art FED 10, wherein a plurality of raised small cathodes 14 are formed on a silicon substrate 12 by means of semiconductor fabrication technology. The small cathodes 14 correspond to a transparent electrode of indio tin oxide (ITO) so as to let fluorescent bodies 18 glow by means of the electrons emitted from the tips of the raised cathodes 14. However, there is still difficulty of manufacturing large-scaled FED 10 of this kind. Moreover, the raised cathodes 14 are usually made of silicon. Although silicon can be easily processed to form various kinds of emitting tips by means of semiconductor technology so as to shrink the geometrical structure, the work function thereof is too high and the conductivity and stability thereof is low, thereby limiting the application of silicon in FEDs. Therefore, other better materials must be selected for the field emitting electrodes.
Because the carbon nanotube has a caliber smaller than a nanometer, and xcfx80 electrons suffuse the cylindrical part thereof, it has a good field-emitting characteristic. Therefore, the carbon nanotube is potential to become high-performance material of field emitting electrodes. Additionally, recent researches show that aligned growth of the carbon nanotube is feasible. Therefore, it can be expected that the chance of manufacturing FEDs using the carbon nanotubes will increase greatly.
Many recent literatures report that the carbon nanotube has a good field-emitting characteristic. It is thus not difficult to manufacture field emitting arrays of low operational voltage. However, it is not easy to keep a stable and reliable field-emitted current of the carbon nanotube. The main reason may be that the structure of the carbon nanotube is not rigid enough to resist large currents. Therefore, it is very important to improve the stability and reliability of the field-emitting characteristic of the carbon nanotube. Although various kinds of thermal processing and film coating have been proposed to resolve part of the problem of material stability, many unstable factors, such as variation of the vacuum environment and change of the geometrical structure of the carbon nanotube due to current flow, still exist.
Accordingly, the present invention aims to propose a FED uniting TFTs and tiny carbon nanotubes to resolve the above problems in the prior art.
The primary object of the present invention is to provide a FED using TFTs to improve the stability of field-emitted currents. The present invention unites TFTs and carbon nanotubes so as to not only improve the stability of field-emitted currents but also control the field emitting cathodes by means of the mature driving circuit of the TFT liquid crystal display (LCD).
Another object of the present invention is to manufacture a FED using the low-temperature poly-silicon (LTPS) technique so that TFTs and the complex driving circuit thereof can be fabricated on a glass substrate. Thereby, the effects of high quality, large area, and low cost can be achieved.
According to the present invention, a field emitting array comprises a plurality of arrays of poly-silicon TFrs. A poly-silicon layer is formed on a glass substrate to be used as sources and drains. Next, an insulating layer is formed thereon, and a gate is then grown on the insulating layer. A plurality of carbon nanotubes corresponding to a transparent electrode of ITO and a fluorescent layer are grown on each of the drains. The carbon nanotubes will operate at a low voltage under the control of the TFTs so as to emit electrons to let the fluorescent layer glow.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings, in which: